Google Street View cars are best known for driving around cities and logging snapshots of the area, which are then posted online and integrated with Google Maps. Google cars had been sniffing some network data - SSID (Service Set Identifier) information and MAC (Media Access Control) addresses - that was then used to help the company get a better fix on the locations of things in order to improve its Web products.

Google had said that it wasn't sniffing other data sent over the networks, but it turned out that this wasn't true.

Google says it was all a mistake.

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"In 2006 an engineer working on an experimental WiFi project wrote a piece of code that sampled all categories of publicly broadcast Wi-Fi data," Google said, "A year later, when our mobile team started a project to collect basic Wi-Fi network data like SSID information and MAC addresses using Google's Street View cars, they included that code in their software - although the project leaders did not want, and had no intention of using, payload data."

Google discovered its error after auditing its Street View WiFi data at the request of the Hamburg, Germany, data protection authority.

The company will now hire a third party to audit the software that Street View used and ensure that all potentially sensitive data was deleted.

Because the Street View cars are usually in motion, they probably would have recorded only snippets of information from open networks, but they could have picked up sensitive data from unencrypted websites, including Google's own Gmail service, which only recently started requiring encrypted (HTTPS) web connections.

"Next week we will start offering an encrypted version of Google Search," Google said.

Google's sniffing is only a problem for people who used open, unencrypted networks. Google wouldn't have been able to log any comprehensible data from networks that used encryption technologies such as WEP (Wired Equivalent Privacy) or WPA (Wi-Fi Protected Access).

"The engineering team at Google works hard to earn your trust," Google said. "And we are acutely aware that we failed badly here."